In general, transmissive type display devices, for example, liquid crystal display devices, comprise a backlight including a light source and a lightguide plate, a liquid crystal cell, and a polarizer provided in each side of the liquid crystal cell. In the backlight, the light emitted from the light source enters the lightguide plate, and is emitted to the liquid crystal cell from the emission surface of the lightguide plate.
The lightguide plate is formed of a resin material such as polycarbonate. In the lightguide plate formed of such a material, the luminance on the emission surface may be reduced or non-uniform since the light emitted from the light source is partially absorbed. The shape of material of lightguide plate may be changed because of heat, load, moisture, etc. When the shape is changed, similarly, the luminance on the emission surface may be non-uniform. Moreover, the absorption of light in the lightguide plate depends on the wavelength. Thus, the color of light emitted from the emission surface may be shifted from the intended color. Further, the color may be non-uniform on the emission surface.
The light emitted from the emission surface of the lightguide plate is lost by two polarizers. To obtain an image with excellent brightness, the intensity of light source should be increased.